Experts
say that of 300 mushrooms, 25% are poisonous, and of all poisonous
mushrooms, 80% are fatal. How many mushrooms are fatally poisonous?

(A)

80

(B)

75

(C)

60

(D)

100

(E)

275

Step 1: Determine what the item is really asking you to
solve.

The item wants you to compare parts of a whole, so you
need to set up a proportion. This item is about double percents,
so you need to apply your knowledge of this concept. Be careful
when taking the percent of the second value.

Step 2: Create an equation.

First you need to find out how many mushrooms are poisonous,
which means taking 25% of 300. Then you need to determine what 80%
of the poisonous mushrooms is, not the total number
of mushrooms. So really, you are dealing with two equations here:

25% of 300 = poisonous mushrooms

80% of poisonous mushrooms = fatally poisonous
mushrooms

You can also write out the order of operations if it helps
you. If you sketch out a plan, the task becomes much easier.

Step 3: Solve the equation.

Set up a proportion to find 25% of 300:

(25%)(300) =

(0.25)(300) = 75

You have 75 poisonous mushrooms.

Now take 80% of 75:

(80%)(75) =

(0.80)(75) = 60

So of 75 poisonous mushrooms, 60 are fatal. Answer choice C is
correct.

Guided Practice

Try this one on your own:

5.

There
are 48 cars in a parking lot. One-third of them are blue, 24 are
red, and the rest are white. What is the ratio of white cars to blue
cars?

(A)

1:2

(B)

1:3

(C)

1:6

(D)

2:3

(E)

5:6

Step 1: Determine what the item is really asking you to
solve.

What do you have to find first to solve this item? What
do you need to find the ratio? Do you have all the numbers?

Step 2: Create an equation.

Do you know the total number of each color? How can you
find the missing numbers? Do you have to find the ratios of all
the cars or just of white to blue?

Step 3: Solve the equation.

Be careful with your numbers. How do you find one-third
of the whole? What is the whole in this item?

Guided Practice: Explanation

Step 1: Determine what the item is really asking you to
solve.

The item ultimately asks you to find the ratio of white
cars to blue cars. That means that you should figure out the actual
numbers of cars, then compare them to each other.

Step 2: Create an equation.

In this case, you need to find out how many white,
red, and blue cars there are in the parking lot. First you need
to find the number of blue cars:

Then find the number of white cars:

white = 48 – (blue + red)

Then you can determine the ratio of white cars to blue
cars.

Step 3: Solve the equation.

First, find one-third of 48, which gives you the number
of blue cars:

Then find the number of white cars:

white = 48 – (blue + red)

white = 48 – (16 + 24) = 8

Now find the ratio of white cars to blue cars:

8 white:16 blue

8:16

You can further reduce these numbers by 8. The
ratio is then 1:2, choice A.

Independent Practice

Turn the page after you solve this item to see our solution.

12.

A
medical research group is testing a new antibiotic on a random sample
of patients. In this sample, 25 patients have some type of food
allergies, 15 have lactose intolerance, 8 have both food allergies
and lactose intolerance, and 3 have neither. What is the total number
of patients in the sample?

Independent Practice: Explanation

Step 1: Determine what the item is really asking you to
solve.

This grid-in item asks you to find the total number of
patients in a sample that includes two sets: patients with allergies
and patients with lactose intolerance. Remember that you also have
patients who have both allergies and lactose intolerance, and those
who have neither.

Step 2: Create an equation.

To solve this item, recall the formula for the total number
of elements, which we introduced in the Essential Concepts section:

Total number = number in set 1 + number in set
2 –
intersection of sets 1 and 2 + number in neither set